iiinova — where your digital self keeps evolving

hforsten @hforsten.com · 14/09/2026

The hardware is described in earlier post. You can find the radar schematic there.

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hforsten @hforsten.com · 14/09/2026

New blog post: Interferometric Synthetic Aperture Radar Drone hforsten.com/interferomet...

hforsten.com

Interferometric Synthetic Aperture Radar Drone

Interferometric SAR with my DIY SAR drone

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hforsten @hforsten.com · 20/02/2026

Yes, if it only needs to work at single frequency. Optimal plating thickness is about 1.57 times skin depth. Of course it would be much worse at lower frequencies than the design frequency.

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hforsten @hforsten.com · 20/02/2026

The peak is caused by reflection from the internal boundary. With non-conductive material the reflection is maximized and the peak is the highest.

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hforsten @hforsten.com · 18/02/2026

This 55 A drone ESC has three nice looking SMD busbars to handle the high current.

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hforsten @hforsten.com · 08/02/2026

If worse conductor is plated on top, the effect is opposite. The effective conductivity of the layered metals can be worse than thick bad conductivity metal.

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hforsten @hforsten.com · 08/02/2026

Did you know that adding a thin plating of good conductor on badly conductive material in RF transmission line can have lower loss at RF than trace made fully of either material by itself? Thought this was a bug in my solver at first, but it's a real physical effect.

With 1 µm copper plating on thick nickel, the effective conductivity is better than if the trace was made fully from copper.

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hforsten @hforsten.com · 27/01/2026

Browser based 2D field solver I've been writing for a while is now up. It calculates characteristic impedance and losses for many common and less common transmission lines.

hforsten.com

2D Transmission Line Field Solver

2D transmission line field solver

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hforsten @hforsten.com · 24/01/2026

I've been writing online transmission line field solver for a while. It will calculate impedance and loss for many PCB transmission lines. Supports solder mask, S-parameter export and more. Missing just last polishing and testing.

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hforsten @hforsten.com · 22/11/2025

Made this simple Vivaldi antenna. It's designed to work from 5.5 to 6.0 GHz and matching looks good at that band.

Vivaldi antenna on FR4 PCB with corrugations and director.

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hforsten @hforsten.com · 04/11/2025

This is getting quite expensive for a hobby project.

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hforsten @hforsten.com · 05/10/2025

SAR image is processed offline. It's just a hobby project.

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hforsten @hforsten.com · 04/10/2025

Synthetic aperture radar vs Gopro.

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hforsten @hforsten.com · 13/07/2025

Wrote code for SAR image antenna pattern normalization and polarimetric calibration (channel imbalance and crosstalk). Image looks very nice now.

Same image after antenna pattern normalization and polarimetric calibration.

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hforsten @hforsten.com · 12/06/2025

It's 10 seconds of data (10,000 radar pulses) and it takes about a minute to process.

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hforsten @hforsten.com · 11/06/2025

I implemented a new SAR autofocus algorithm and now the image generation is both better and faster. It's about as well focused as it can be now.

Polarimetric synthetic aperture radar image

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hforsten @hforsten.com · 05/06/2025

Fixed some bugs in my SAR processing code and now fast factorized backprojection generates a visually identical picture to the normal backprojection, but over 10 times faster. That's huge because normal backprojection was already extremely quick and there's still room for optimization with FFBP.

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hforsten @hforsten.com · 01/06/2025

I also implemented generalized phase gradient autofocus earlier this week. I haven't seen any open source implementations of it before. It works quite well with this kind of short range SAR image, but my earlier minimum entropy optimization method still gives better results.

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hforsten @hforsten.com · 01/06/2025

Found motivation to write some SAR processing code. Fast factorized backprojection generates several small polar format images and then interpolates them to one big image. It's faster, but has slightly worse image quality due to all the interpolations.

Global backprojection vs fast factorized backprojection image quality. The biggest difference is larger sidelobes on the brightest target in the FFBP image.

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hforsten @hforsten.com · 30/05/2025

Just some random ones I had lying around. The bigger one is labeled: "XRRH6*10*3"

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hforsten @hforsten.com · 29/05/2025

That's the measured S21 from input to the isolated port when the other ports are terminated. Reflection of the termination is not de-embedded, but it's better than -25 dB over the whole frequency range.

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hforsten @hforsten.com · 29/05/2025

I made this new dual directional bridge coupler using 1 mm diameter coaxial cable. It's a little bit better than the previous one I made using 2 mm coaxial cable and much more annoying to solder.

Thru, coupled, and isolated port S21 with other ports terminated.

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hforsten @hforsten.com · 28/05/2025

It works really well. Loss is low and matching is excellent.

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hforsten @hforsten.com · 28/05/2025

Bought this thru with 3.5mm RF connectors. It's air filled with just a thin see-thru membrane holding the center pin in place.

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hforsten @hforsten.com · 21/05/2025

Some new RF connector test PCBs. Nameless low-cost solderless 3.5 mm connector on the left and CONSMA003.062 clone on the right. Both work okay.

Two test PCBs with 3.5 mm and SMA connectors

3.5 mm and SMA connector S-parameters with 11 mm line

3.5 mm and SMA connector time domain response with 11 mm long line

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hforsten @hforsten.com · 15/05/2025

It would require hole and threads in the case for the connector making the case more expensive. Connector would also need to be soldered to the PCB while attached to the case, not very handy for a prototype.

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hforsten @hforsten.com · 06/05/2025

It's this one: www.aliexpress.com/item/1005006.... Calibration coefficients are not included.

aliexpress.com

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hforsten @hforsten.com · 06/05/2025

Bought this VNA calibration kit with 3.5 mm connectors. Looks good considering the 60€ price tag.

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hforsten @hforsten.com · 15/04/2025

It's a very nice looking chip, but too expensive. Sure if someone else pays.

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hforsten @hforsten.com · 10/04/2025

Just found an annoying flaw with this cheap bias-T. The connector is threaded in the case and if the cable is tightened with a torque wrench, it can unscrew also the SMA connector when removing the cable.

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hforsten @hforsten.com · 05/04/2025

That could work in some situations, but I don't think it will work here. The connection between SMA connector and the case is not tightened so it wouldn't be compressed. Mating surface also isn't a full circle, just the upper part of the connector.

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hforsten @hforsten.com · 05/04/2025

I thought this might be an issue during design. The proper fix would be to use a bulkhead SMA connector but that complicates the mechanical design and I didn't think it was worth the trouble.

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hforsten @hforsten.com · 05/04/2025

There's a tiny gap between the case and SMA connector that radiates a little if not sealed. Putting some solder wick in the gap seals it nicely but there has to be some more elegant method.

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hforsten @hforsten.com · 04/04/2025

No, never thought there was enough interest to bother with that. This is fully self funded.

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hforsten @hforsten.com · 04/04/2025

CNC machined case for the VNA just arrived. Machining quality is good and it looks stylish (very important). The cost was $140 including shipping and taxes, much cheaper than I initially feared.

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hforsten @hforsten.com · 24/03/2025

Mechanical and temperature stability are currently the factors limiting the measurement accuracy. Electronics should be way more accurate than what I can currently measure.

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hforsten @hforsten.com · 24/03/2025

VNA also works as a temperature sensor and strain gauge.

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hforsten @hforsten.com · 24/03/2025

I doubt it's much better. This part really should be CNC machined from aluminium so that it would also function as heatsink.

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hforsten @hforsten.com · 24/03/2025

It does get quite hot. FPGA internal temperature sensor says it's 70 degrees Celsius. I think the RF parts might run even hotter. 3D printed enclosure is a really poor heatsink.

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hforsten @hforsten.com · 24/03/2025

This turned out to be slightly more difficult than I first thought. Foil tears easily and even a small tear will affect the isolation. It might require multiple layers to get a tear free lining. Foil also needs to be glued down so that it doesn't move around or it will increase drift of the VNA.

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hforsten @hforsten.com · 23/03/2025

All drills were supposed to be 0.3 mm. Most pad diameters are 0.45 mm, but some are 0.40 mm. This used to be fine previously for no extra cost. I found few unintentional 0.2 mm drills with 0.5 mm pads and apparently this caused the extra charge?

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hforsten @hforsten.com · 23/03/2025

It requires 5.8 ns input data valid eye with 10 ns clock period. Clocking the data with suitably phase shifted clock should work. Currently I'm not doing that and have some timing violations, but it works despite them.

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hforsten @hforsten.com · 23/03/2025

The main issue with it is that the specified setup and hold timings are hard to fulfill. Other than that it works fine.

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hforsten @hforsten.com · 22/03/2025

The same measurement with my previous VNA (hforsten.com/improved-hom...), the new VNA has much better performance. 70 dB improvement in isolation + dynamic range at 8 GHz.

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hforsten @hforsten.com · 22/03/2025

Got the VNA software working and made some first measurements. With shorts at both ports the isolation is excellent >100 dB and the VNA works well at least up to 10 GHz with slight dynamic range reduction at higher frequencies.

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